Abstract 652: Increased Gα o Expression Plays a Pivotal Role in the Progression of Heart Failure by Impairing Ca 2+ Handling

Abstract

Background: A transcriptional repressor, neuron restrictive silencer factor (NRSF), maintains normal cardiac function and electrical stability. Transgenic mice expressing a dominant-negative mutant of NRSF in their hearts (dnNRSF-Tg) exhibit systolic dysfunction and premature death due to lethal arrhythmias like human dilated cardiomyopathy(DCM). Underlining mechanisms remain to be elucidated, however. Purpose: To clarify how NRSF maintains normal cardiac homeostasis. Methods and Results: cDNA microarray analysis of dnNRSF-Tg and newly generated cardiac-specific NRSF knockout mice (NRSFcKO), which show similar cardiac phenotypes to those of dnNRSF-Tg, revealed that cardiac gene expression of GNAO1 that encodes Gα o , a member of inhibitory G protein Gα i family, is increased in both dnNRSF-Tg and NRSFcKO ventricles. ChIP-seq analysis, reporter assay and electrophoretic mobility shift assay identified that GNAO1 is a direct target of NRSF. In dnNRSF-Tg, pharmacological inhibition of Gα o by pertussis toxin improved systolic dysfunction and knockdown of Gα o by crossing with GNAO1 knockout mice improved not only systolic function but also frequency of ventricular arrhythmias and survival rates. Electrophysiological analysis in ventricular myocytes obtained from dnNRSF-Tg demonstrated that genetic reduction of Gα o ameliorated abnormalities in Ca 2 + handling, which include increased current density in surface sarcolemmal L-type Ca 2 + channel, reduced content of sarcoplasmic reticulum Ca 2+ and lowered peak of Ca 2+ transient. In addition, genetic reduction of Gα o attenuated increased phosphorylation levels of CAMKII and RyR2 in dnNRSF-Tg ventricles, which presumably underlies the improvement in Ca 2 + handling. Furthermore, we identified increased Gα o expression in ventricles of heart failure model mice induced by transverse aortic constriction and cardiac troponin T mutant DCM model mice, in both of which, genetic reduction of Gα o ameliorated cardiac dysfunction. Conclusions: We found that increased expression of Gα o , induced by attenuation of NRSF-mediated repression, plays a pivotal role in the progression of heart failure by evoking Ca 2+ handling abnormality. Gα o is a potential therapeutic target for heart failure.